The invention involves photopolymerizable compositions for image recording, containing an addition-polymerizable, ethylenically unsaturated compound, a photoinitiator or a photoinitiator system and at least one polymeric binder, wherein at least one of these binders is made from a copolymer of, respectively, one or more different structural units A and B and at least one additional structural unit containing carboxyl groups. Photopolymerizable compositions are extensively used in image recording materials, particularly in the production of photoresists, solder resists and printing plates.
Photopolymerizable resist materials are known, for example, from U.S. Pat. Nos. 3,469,982 and 3,547,730, which describe a film resist with a sandwich structure in the form of a photopolymerizable layer between a cover sheet and a temporary support. This film resist can, for example, be laminated on a copper base, exposed imagewise and developed, whereby a resist layer is formed.
The resist layer thus produced can now be selectively etched, electroplated or treated with solder on the substrate. Particularly high demands are placed on photoresist films if they are used as solder resists. In this case, the developed, photopolymerized layer must withstand temperatures up to 300.degree. C. According to the current state of the art, such solder resists can be made by spraying, coating or calendering liquid compositions on a substrate or also by laminating a dry film on a substrate.
The described photoresist films consist usually of a temporary or permanent support, a photopolymerizable layer, which contains a polymeric binder, addition-polymerizable compounds and a photoinitiator, and a cover layer. After imagewise exposure and optionally, after lamination on a substrate, the cover layer can be removed and the photopolymerizable layer can be developed. Many photopolymerizable compositions can be developed with organic solvents, many with aqueous solutions.
Frequently, the polymeric binders of such photopolymerizable image recording materials, particularly those that are aqueous-developable, contain acid functions, primarily carboxyl functions. However, these groups are disadvantageous in many processing steps. In the case of photoresists, delamination of the resist is observed in alkali etching or gold plating, in the case of solder resists, inadequate moisture and insulation properties.
In particular, completely aqueous developable photopolymer systems with high wash-off rates and, in some cases, rapid stripping behavior, show, because of their hydrophilic properties, weaknesses in other processing steps, for example, narrow development latitude, stripping in alkali etching and in gold plating or inadequate climatic resistance.
In the field of photoresists, modification of the carboxyl groups with melamine compounds to overcome the named disadvantages is known (EP 01 15 354 and U.S. Pat. No. 4,247,621). However, the addition of the melamine compounds can decrease the light sensitivity of the photopolymerizable compositions, so that such compositions require longer exposure times. Furthermore, many of these compounds tend to crystallize on long storage of the photopolymerizable compositions, so that recording materials prepared therefrom cannot be used.